1. Field of the Invention
The present invention relates to a multi-lens imaging apparatus, and more particularly to a multi-lens imaging apparatus for providing a highly fine single image by synthesizing two images having been obtained by imaging a common object through two sets of imaging systems.
2. Related Art
Principles of a multi-lens imaging apparatus have been proposed as shown in FIG. 1 for providing a highly fine single image by synthesizing two images having been obtained by imaging a common object through two sets of imaging systems. Namely, in such principles of the multi-lens imaging apparatus, a left-side imaging system 110L and a right-side imaging apparatus 110R are provided at the ideal situation for imaging an object 101 with a 1/2 pitch of divergence of sampling point in space phase therebetween. An image IL obtained by the left-side imaging system 110L and an image IR obtained by the right-side imaging system 110R are synthesized by a microprocessor (hereinafter referred to as "CPU") 120 to provide a highly fine single output image IOUT compared to a case where the object is imaged by a single imaging system.
FIG. 2 is a drawing for explanation of the basic disposition of the left-side imaging system 110L and the right-side imaging system 110R.
The left-side imaging system 110L is composed of a left-side imaging optical system 111L and a left side image sensor 112L, and in the same manner, the right-side imaging system 110R is composed of a right-side imaging optical system 111R and a right-side image sensor 112R. The left-side imaging optical system 111L and the right-side imaging optical system 111R have equivalent specifications, and are composed of zoom lens. Also, the left-side image sensor 112L and the right-side image sensor 112R have equivalent specifications, and are composed of imaging tube such as sachicon, or solid-state imaging element such as CCD. The left-side imaging system 110L and the right-side imaging system 110R are disposed on positions where they substantially .intersect each other at a point O on an object surface 102, and are linearly symmetrical with respect to a normal line O-O of the object surface 102. In this case, when angles formed by optical axes LL, LR and the normal line O-O of the object surface 102 are respectively referred to as .theta., the expression 2.theta. is defined as a convergent angle.
In this conventional multi-lens imaging apparatus, when the object distance is changed, the imaging is performed for example by changing the convergent angle 2.theta. by rotating the left-side imaging system 110L and the right-side imaging system 110R in accordance with the change of the object distance with x mark as a center in FIG. 2.
However, in the aforementioned conventional multi-lens imaging apparatus, as the object distance becomes shorter (i.e. the convergent angle 2.theta. becomes larger) a photosensitive surface (image surface) at periphery portions of the left-side image sensor 112L and the right-side image sensor 112R become out of conjugation so as to increase the unsharpness of the image. This problem will now be described in detail with reference to FIG. 3.
If, with respect to a material point P1 on the object surface 102, there are designated respectively: unsharpness amount on a flat surface 200 conjugated with the photosensitive surface at the periphery portion of the right-side image sensor 112R, by .delta.; a distance from a front-side main point H of the right-side imaging optical system 111R to the flat surface 200, by S0; a distance from the front-side main point H of the right-side imaging optical system 111R to the object point P1, by S1; and an effective pupil diameter of the right-side imaging optical system 111R, by D, they can be represented by the following equations: EQU .delta./D=(S0-S1)/S1 (1) EQU S0-S1=S0/(1+D/.delta.) (2)
Further, if the unsharpness amount with respect to the object point P1 on the photosensitive surface at the periphery portion of the right-side image sensor 112R is designated by .delta.' and the imaging magnification (lateral magnification) of the right-side imaging optical system 111R is designated by .beta., they can be represented as follows: EQU .vertline..delta.'.vertline.=.vertline..delta..multidot..delta..vertline.(3 )
If the length of a line segment from the object point P1 to the optical axis LR is designated by .eta., they can be represented by: EQU S0-S1=.eta..multidot.tan (.theta.) (4)
Furthermore, if the length from an intersection of a line connecting the front-side main point H of the right-side imaging optical system 111R to the object point P1 with the flat surface 200 to an intersection P0 of the optical axis LR with the flat surface 200, they can be represented by: EQU .eta./y=S1/S0 (5)
Therefore, the equation (5) can also be expressed as follows: ##EQU1## Substituting the equation (2) for (S0-S1), the equation (6) can be represented as follows: ##EQU2## Since the equation (4) can be alternatively expressed as: EQU tan (.theta.)=(S0 S1)n (8)
As a result, the equations (2) and (7) can also be expressed as follows: EQU tan (.theta.)=S0/{y .multidot.(D/.delta.)} (9)
On the other hand, a focusing distance of the right-side imaging optical system ! 11R is designated by f and the F number is designated by F, the following relationship exists: EQU D/.delta.=(f.multidot..beta.)/(F.multidot..delta.') (10)
Here, the following relationship exists: EQU SO=f.multidot.(1/.beta.-1) (11) EQU y=y'/.beta.(12) (12)
Accordingly, the equation (9) can be expressed as follows: ##EQU3## Therefore, the following relationship exists: EQU .delta.'=y'.multidot.tan (.theta.)/{F.multidot.(1/.beta.-1)}(14)
The unsharpness of amount .delta. represented by the equation (14) takes place at the photosensitive surface of the periphery portion of the right-side image sensor 112R to degrade the contrast of the image particularly in case of short-distance imaging. The same is true in the left-side image sensor 112L.